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000
AGNT40 KWNM 120758
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
300 AM EST TUE 12 DEC 2017

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Atlantic Ocean W of 50W from 30N to 50N.

The 02Z Ascat overpass clearly delineated the stationary front
across the Gulf of Maine and indicated north winds to 20 kt just
poleward of the front. Elsewhere there were also some winds to
20 kt off the Georgia and South Carolina coasts. The 00Z models
continuted in excellent agreement across the west Atlantic for
the next 48 hours or so. The potential for hazards becomes
highly likely today ahead of strong low pressure that will move
from the lower Great Lakes into the Canadian Maritimes today
into Wednesday, accompanied by a strong cold front passing east
across the NT1 and NT2 waters. Over the past few runs, the
models have trended stronger both the prefrontal winds as well
as with the widespread prolonged gales west of the front in the
strong cold air advection tonight through Wed night. The 00Z GFS
is the strongest of the models with the winds and now even shows
some southerly winds reaching storm force across the nothern
outer NT2 zones tonight. Although will likely see fairly large
areas with storm force gusts across these outer waters, will cap
the winds at 45 kt as the GFS only indicating the low level jet
reaching 55 kt or perhaps 60 kt briefly. We continue to have
well above average forecast confidence that widespread gales
will develop across all of the offshore waters associated with
the cold front today and extending through at least Wed night.
As was noted above, storm force wind gusts are likely especially
across the outer NT2 zones near the Gulf Stream where deep
convection is expected to develop this afternoon into tonight.
Used a stability smart tool for the wind grids through Wed
night, which places the 00Z GFS 10m winds across the stable
areas, and the higher GFS first sigma level winds across the
unstable areas, which in this case is across all the offshore
zones behind the cold front.

As the strong low lifts north, widespread gales will diminish
gradually Wednesday into Wednesday night from southwest to
northeast over the offshore waters. The 00Z models then all
indicate a clipper type low pressure system will emerge off the
Mid Atlantic coast early Thu. As was the case with the previous
couple runs, the 00Z GFS continued to trend stronger with this
feature and like the 18Z/11 run is again advertising storm force
winds across ANZ905 and ANZ910 Thu. 00Z GFS/NAM low level lapse
rates indicate that the low level environment will still be
quite unstable Thu, so some there is some potential for the
sustained winds to briefly reach storm force across these outer
zones Thu. The 00Z ECMWF also trended toward the stronger GFS,
and now is also further north with the track of the low, similar
to the GFS. Based on this trend, am favoring the stronger GFS
and will go ahead and upgrade the gales to storm force across
those outer zones. This low should rapidly accelerate northeast
passing south of the Canadian Maritimes late Thu and Thu night.

Late in the period Fri/Sat, our forecast confidence wanes as the
models continue to have difficulty coming to a consensus with
how amplified the next upper level trough will be moving to the
eastern seaboard. The 00Z GFS continued to be the strongest
solution and also is less progressive than the ECMWF/UKMET. The
latter models come into excellent agreement at 00Z. However, the
latest GEFS and ECMWF EPS both suggest that the ECMWF/UKMET
deterministic runs are too weak. Given the uncertainty, we are
favoring the WPC medium range winds, which were based on a blend
of the GEFS and ECMWF EPS means. However, out of deference for
the consistently stronger GFS and with both the ECMWF and UKMET
near or at gale with the post frontal winds Fri night into Sat
night, will go ahead and boost the WPC winds slightly to get
some marginal gales across the outer waters at that time.

.Seas...Both the 00Z Wavewatch III and 00Z ECMWF WAM were well
initialized with the west Atlantic wave heights at 06Z and are
generally within 3 ft or so of each other across the offshore
waters through Fri. Thereafter, the models diverge significantly
with the GFS significantly stronger than the ECMWF with the Fri
night/Sat night system. Will be using an even blend of the
aforementioned guidance for the wave height grids through Fri
before transitioning solely to the 00Z ECMWF WAM beginning Fri
night.

.EXTRATROPICAL STORM SURGE GUIDANCE...The consensus of the
ESTOFS and ETSS guidance suggests any storm surge along the
Maine coast to the Bay of Fundy will be around 1 ft this evening
and tonight. The 00Z ETSS is slightly higher than the 00Z
ESTOFS, but only a few tenths feet.

.WARNINGS...Preliminary.
.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale today into Wednesday night.
.ANZ805...Georges Bank west of 68W...
     Gale Wednesday into Wednesday night.
.ANZ900...Georges Bank east of 68W...
     Gale tonight into Wednesday night.
.ANZ810...South of New England...
     Gale tonight into Wednesday night.
.ANZ815...South of Long Island...
     Gale tonight into Wednesday night.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale tonight into Wednesday night.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale tonight into Wednesday night.
     Gale Possible Thursday.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale today into Wednesday night.
     Gale Possible Thursday.
     Gale Possible Saturday.
.ANZ905...The Great South Channel to the Hague Line...
     Gale tonight into Wednesday night.
     Storm Possible Thursday.
     Gale Possible Thursday night.
     Gale Possible Saturday into Saturday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale today into Wednesday night.
     Storm Possible Thursday.
     Gale Possible Thursday night.
     Gale Possible Saturday.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles
Light...
     Gale tonight into Wednesday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck
Beach Light...
     Gale today into Wednesday night.
     Gale Possible Thursday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras
Canyon...
     Gale today into Wednesday night.
     Gale Possible Thursday.
     Gale Possible Friday night into Saturday.
.ANZ830...Inner Waters from Currituck Beach Light to Cape
Hatteras...
     Gale today into Wednesday.
     Gale Possible Thursday.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale today into tonight.
     Gale Possible Thursday.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale today into Wednesday.
     Gale Possible Thursday.
     Gale Possible Friday night into Saturday.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale today into tonight.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale today into tonight.
     Gale Possible Friday night.

$$

.Forecaster Clark. Ocean Prediction Center.



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